A device and a method of the forenamed general type are known from EP 0 428 873 B1. Devices and methods of this type are used to make, using a liquid material, for example a molten material, and a gas, for example air, a foam in which the material and the gas are mixed intensively with each other. Foams made in this way are needed for a great many applications, including adhesive foams, foam sealants, foam packaging material or the like.
These devices and methods can produce homogeneous foams, i.e., foams having a pore size that falls within a predetermined range and which maintain this pore size range in all areas of the foam. Often an effort is made to achieve as small a pore size as possible and to have the maximum possible number of pores present per unit of foam volume. EP 0 428 873 B1 proposes a system for this purpose in which the flow-through of the liquid material is measured with a liquid flow metering device and the flow-through of gas is measured by means of a gas flow measuring device. Two signals based on these measurements are compared to each other, and target data are used to determine a target gas content which is determined by calculating and setting a differential gas value. While this system is able to achieve a satisfactory foam quality for a number of types of foam, the system has a complex control technique which also results in little system variability.
From EP 0 651 677 B1 a device and a method for applying foam coatings are known in which an effort is made to increase the foam quality by supplying heated air to the foam laterally from both sides in an applicator head and thereby achieving additional mixing. With this additional supply of air it is possible to better control the beginning and ending of application, and the quality of the foam itself is also improved. However, the device and method from EP 0 651 677 B1 have the disadvantage that a relatively complex design of the foam applicator head is necessary, and in addition the variability of the device is limited with regard to different types and compositions of foam.
Finally, from EP 0 220 450 B1 a method and a device for foaming high-viscosity polymer materials are known, in which a liquid and a gas are mixed together in a mixing device that includes two rotating shafts with mixing elements formed on them. While this mixing device is able to achieve a homogeneous foam, it has the disadvantage that in particular the beginning and the end of the formation of foam are accompanied by a reduction of the foam quality, and in addition the system has little variability with regard to various operating modes, foam types and foam compositions.
It would therefore be desirable to address remaining challenges in this area, such as by providing a device and a method which exhibit greater variability in the production and application of foam material, and at the same time are able to produce equal or even higher foam quality than known systems.